How do I figure out how much head loss I have to figure out what pump to buy?

[DennisP]

Hey guys, unique situation here, as I am putting up an above ground pool, but running PVC piping in-ground to have the pump and filter mounted near the garage... I am putting up a 27' x 54" AGP.

Basically will have 2" PVC in-ground, 73ft away from the equipment. Dual runs of 2" PVC (one for suction, one for return). I am planning on running a Sta-Rite sand filter (model T-210WF) to start, but will probably go with either a cartridge or DE filter eventually. I already have the sand filter.

I am burying the PVC 1.5-2ft in the ground. I plan on coming up by the pool and using flexPVC to plumb from the risers to the pool. Planning on only 1 skimmer/suction to start and going with just a single return to start. I may switch that to multiple skimmers/returns in the future, but to start just singles.

So, I have 73ft of suction PVC, 2 sweep 90s going to the risers (one by the pump, one by the pool) and then the 2ft or so going up to the pump or flexPVC going to the pool.

Now, am I looking at over 90ft of total head loss???

As far as pump I figure I will probably need an in-ground pump, since above ground pumps don't expect too much head loss at all, or what?

 

[mas985]

Head loss is not "equal" to the length of runs but it is dependent on it. The calculations are quite involved but you don't really need to figure out head loss. The distance is not such a concern since you are using 2" pipe and most AG pumps will do fine with that setup including a Pentair OptiFlo, Dynamo or Hayward Matrix would work fine. You don't need an IG pump as long as the priming height is not more than a few inches. Is there an elevation rise from the pool to the equipment?

 

[DennisP]

No elevation rise at all, if anything there is an elevation drop of about 3-6 inches at least.

So, I could basically go with any decent 1hp to 1.5hp pump and be good?

Wouldn't 3/4hp be too small?

The filter has a 44GPM filtration rate.

 

[mas985]

With such a small filter, you want a small pump so a 3/4 HP would be fine but I think only the Dynamo comes in a 3/4 HP two speed.

 

[DennisP]

Well, as a followup...

I was concerned about having enough suction for an automated pool cleaner, so I was still hedging on at least a 1hp pump. Also since I wanted to stay with the wiring I have I was looking at something 230v, so I was looking at in-ground 1hp setups, but budget-wise I am over-budget on this build so I was expecting to go with a "Mighty Niagara" branded 1hp pump (with a rated amp draw that was probably more like a 3/4hp pump with a higher rated impeller, which only means it would be stressed that much more)...

Well, just as I was about to order this morning I came across a great deal on a Pentair Dynamo 1.5hp 340206 2-speed 115v pump. Looking at the label it has that part number, but is rated at 11amps on high, 2.9amps on low. Which is strange because the Pentair specs are 16.4/4.4 for the 340206, but looking at the performance curves the 1hp and the 1.5hp are rated identical and the 1hp is rated at 11/2.9. So I guess they just play games with the ratings labels.

I will need to mess around with the wiring to reconfigure for 120v. Not such a big deal I guess, just kinda a PITA now.

Now I need to decide if I am going to put in either a booster pump for a pressure-based pool cleaner, or just get another pump for a suction-based cleaner. I have enough room on the equipment pad, so I am considering using dual filters, one off the skimmer and the Dynamo pump on low 24/7 (probably a DE or cartridge filter for that one) and then another 1.5hp pump on a timer probably set for an hour or two in the mornings for the automatic cleaner with the sand filter I have now. Any problems with that kind of configuration?

 

[mas985]

Motor ratings do not reflect actual energy use. They only specify the maximum operating conditions for the motor. So it is impossible to compare pumps with just the motor label ratings.

The 1 1/2 HP Dynamo is an SPL (special) rated pump so yes, it is identical to the 1 HP up rated Dynamo.

Now I need to decide if I am going to put in either a booster pump for a pressure-based pool cleaner, or just get another pump for a suction-based cleaner.

Why? A single pump should be able to handle a suction cleaner.

 

[golfinglenn]

For future reference, head loss, or head pressure is used to figure vertical pressure, not horizontal or length of pipe issues, which would be considered friction loss. To figure head pressure you need to take the elevation change in feet and multiply by .433. So if your pump is 10 feet above your pool you would need a pump that can overcome 4.33 lbs of negative pressure.

Friction loss is entirely dependent on size and type of pipe, and how many gpm is flowing through the pipe. With the amount of water flow with a pool, I don't think friction loss is an issue. I could give a whole hydraulics class, but that would just put everyone to sleep and there would be a test afterwards :-(. ;-).

Glenn

 

[mas985]

You are preaching to the choir: http://www.troublefreepool.com/threads/830-Hydraulics-101-Have-you-lost-your-head

 

[DennisP]

Motor ratings do not reflect actual energy use. They only specify the maximum operating conditions for the motor. So it is impossible to compare pumps with just the motor label ratings.

The 1 1/2 HP Dynamo is an SPL (special) rated pump so yes, it is identical to the 1 HP up rated Dynamo.

Why? A single pump should be able to handle a suction cleaner.

Yeah, I figured the whole HP rating thing doesn't matter much and actual performance graphs (from real companies that post realworld factual outputs) matter more. The amp rating is all that really matters to me in regards to wiring.

In regards to the cleaner, I was thinking I would want to have not only the skimmer cleaning the surface, but also a separate automated floor cleaner. Both probably on different schedules (like the skimmer running during a set schedule, say 15 minutes every couple of hours) and the floor cleaner running from say 5am until 8am or something... Just flexibility more than anything... Using a single pump would mean I would have to make a choice one way or another, whereas another timed pump would give me flexibility. Having the cutouts right by the pumps allow me to easily disable the cleaner if I am not going to run it for some reason. The timers are in the basement near the electrical panels, not by the equipment, so running down there to switch off breakers or to manually mess with the timers is something I don't want to do on a regular basis.